Various types of control systems have for many years used dead bands in their operation. A dead band normally is defined as the range of values of a measured variable to which an instrument or system will not effectively respond.
The use of dead bands can be applied to many types of instruments or systems, but is particularly of value in the heating and cooling control art. Ordinarily a dead band will exist between the operation of a heating or cooling function, or will be present between directions of rotation or movement of an electromechanical device, such as a motor, in the positioning of some element in a heating or cooling system.
Typically dead bands have been provided in electronic systems by the use of operational amplifiers, bridges, and resistances to establish bridge control values. When this type of an arrangement is used the width of the dead band is sometimes quite critical. A narrow dead band is more sensitive to electronic noise, whereas a wide dead band reduces the resolution of the control system. Presently this type of dead band characteristic is generated by using operational amplifiers with external resistors which may, in some cases, require trimming. This type of a system is quite expensive to manufacture and accurately control.